[BUG]Plantgene data disks lose their plantgene data after a while for no discernible reason.

[Ravellon]

Reproduction:

Basically extract any plant gene data from a seed into the disk with plant DNA manipulator, leave it be for a while and check it. It will eventually lose the data.

The variable is "gene" and is unique to disk/plantgene subtype of disks as defined in gene_modder.dm
When it records data it puts a datum reference there. But eventually the variable turns null. That's the only change that happens to the disk as the disk's name remains the same.